In the event of a hijacking, the pilot, or a ground controller issues a command that causes a locked compartment in each passengers armrest to open up revealing a weapon of some sort. Club, knife, net and trident, sharpened high heel shoe, habrick in a sock, etc. Passengers can form an instant mob
to overcome any resonable hijacking attempt.

Interesting idea. However, an unarmed group can now get through security easily; once on the plane, a couple of them make a hijack attempt. When the pilot triggers the system, the rest of the group arm themselves, take hostages at knifepoint (or halfbrickpoint, a bit trickier)...? [-]